We propose to examine some of the behavioral factors that influence the effects of narcotic analgesics by quantifying the contribution of sensory and response variables to drug-induced alterations in the discrimination of environmental stimuli which can be painful and to stimuli which probably are not painful. In this respect, we will examine discrimination of electric shock stimuli and thermal stimuli. Our major consideration will be the measurement of the degree to which drug-induced alterations in behavior under the control of these discriminative stimuli are determined by the sensory and/or response aspects of the situation. To meet this goal, we will use two procedures in which sensory and nonsensory (response) variables can be manipulated and thereby examine the extent to which these variables determine a drug's effect. In the shock titration procedure, the intensity of shock squirrel monkeys tolerate will be determined under a variety of conditions. In the discrimination procedure, squirrel monkeys will discriminate between the presence and absence of electric shock of thermal stimuli as well as between different intensities of these stimuli. In addition to investigating the behavioral mechanism of action of prototypic narcotic analgesics (morphine, pentazocine) and of comparision drugs not thought to produce analgesia (diazepam and chlorpromazine), these procedures will be used to examine some new drugs which are thought to have analgesic effects. These include the morphine-like narcotic antagonist, buprenorphine and the kappa agonists, ketocyclazocine and ethylketocyclazocine, all of which appear to have low abuse potential.